JP2010-209946A discloses a technique where an auxiliary transmission mechanism with two forward speed stages of a first speed stage and a second speed stage that has a small transmission gear ratio compared with the first speed stage is disposed in series with respect to a continuously variable transmission mechanism.
In the technique disclosed in JP2010-209946A, when a gear is shifted from the above-described first speed stage to the above-described second speed stage, a changeover of a first engagement portion (first speed clutch) and a second engagement portion (second speed clutch) is performed in a torque phase. In an inertia phase subsequent to the torque phase, the transmission gear ratio of the auxiliary transmission mechanism is up-shifted. The transmission gear ratio of the continuously variable transmission mechanism is down-shifted by an amount of the change of the transmission gear ratio of the up-shifted auxiliary transmission mechanism to keep the transmission gear ratio of the entire continuously variable transmission mechanism and auxiliary transmission mechanism constant. However, since a driving force of the first engagement portion and a driving force of the second engagement portion are different from one another, and in the torque phase, the driving force changes to the smaller side, a negative acceleration generates in a vehicle front-rear direction. This generation of the negative acceleration in the vehicle front-rear direction causes a driver to feel a shock.
It is an object of the present invention to reduce a shift shock during a gear shifting from the first speed stage to the second speed stage of the auxiliary transmission mechanism.